Studies for enhancing emission efficiency of an organic electroluminescent device (organic EL device) are made actively. In particular, studies of development of new light-emitting materials for efficient emission are made variously. Among them, a light-emitting material using an exciplex formed of a combination of an acceptor compound and a donor compound has a possibility dial, by combining a suitable acceptor compound and a suitable donor compound, the energy difference ΔEst between an excited triplet energy level and an excited singlet energy level can be reduced as compared with a light-emitting material having an acceptor and a donor in one and the same molecule, and use of the exciplex as a delayed fluorescent material is now under investigation.
For example, PTL 1 proposes a delayed fluorescent material containing a mixture of an acceptor compound and a donor compound in which the degree and the relationship of the excited triplet energy T1A and |LUMOA| of the acceptor compound, the excited triplet energy T1D and |HOMOD| of the donor compound, and the excited singlet energy S1 of the exciplex are specifically defined. This patent reference confirms high emission efficiency of the light-emitting device using the delayed fluorescent material.